thank you, it's only a little job on the lathe.
srew: from a honda motorbike (to hold some plasic parts)
T-nut: it was a knurled nut, made a bit shorter and thinner
plate: alu plate and a lot of filing to get this shape (really bad idea from deeluxe)
it's also difficult to get the right length of the system. that means the screw touches the T-nut with its ligament, so you can tighten without clamp the alu plate. but you can't adjust the distance between the shell parts with the screw, you have to tune the length oft the T-nut.
somewere I have a drawing with the exact measuremts, should I post it?